It depends where the split is, it's possible to
drill and plate it , if the split is on a flat area.
This involves drilling a small hole at either end
of the split which stops it travelling further. Then
putting 2 metal plates over the area, one above and
one below. drilling and bolting them together with a
sealant spread on them.
If it's on a seam it needs plastic welding with the
correct HDPE welding kit. Nothing else will adhere
to HDPE, it's too waxy a plastic.